Karma is a test runner and you can choose/mix your own test frameworks such as Jasmine, mocha etc.

Generally, you can use karma and jasmine/mocha for unit testing, end-to-end testing etc.

Manual testing is required all the time in terms of any new features/enhancements/upgrades etc whenever you change something and test the changed code/UI/functionality.

But the automated testing with karma said above are required to avoid the regression testing effort where you didn't change the code directly but there should be an indirect impact to find any of the new changes broken the existing functionality.

When you automate this karma/jasmine testing in to the CI/CD build tools like TeamCity/Bamboo/Jenkins etc, you could find the regression impact as early as possible (most probably on the development phase) instead of letting it to go into UAT/Staging/Pre (or) post production phases.

Thus to summarize,manual testing is always required to test the immediate changes and automated test cases are required to test the regression impact.

At minimum, unit testing should be required and having user acceptance testing and end-to-end testing would be best to cover.

Hope it clarifies your question :-)

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